The invention relates to a microcontroller comprising a command decoder.
Single-chip microcomputers which are generally used for controlling apparatuses and in which CPU, memories and ports are integrated on a chip are understood to be microcontrollers. The CPU comprises in known manner a command decoder which decodes the loaded commands and performs a run-off control in order that the commands are carried out by the computer.
Microcontrollers are programmed in a machine-dependent assembler language. In the known assembler languages, all assembler commands, with the exception of the conditional program steps, are executed independently of data. When different operations must be performed in dependence upon given data, this is possible in conventional microcontrollers only with a considerable programming effort. The condition to be realized must then be extensively encoded in the assembler. When, for example, generic pointers in a high-level language compiler are to be programmed by means of different assembler commands dependent on the addressed memory, this requires a high programming effort or, by substitution, a considerable number of hardware components for reconfiguring the memory.
Based on this background, it is an object of the present invention to improve a microcontroller of the type described in the opening paragraph as regards its functionality and to simplify the programming.
This object is achieved by a microcontroller as defined in the characterizing part of claim 1. Advantageous embodiments are defined in the dependent claims.
The microcontroller comprises a command decoder as well as at least one memory to which the command decoder has direct access. The command decoder is adapted to decode at least one conditional command, the result of the decoding of the conditional command depending on the contents of the memory to which the decoder has access. When the command decoder thus loads a conditional command, it checks the contents of the memory to which it has access and, in dependence upon the result of this check, it supplies a machine command from a series of possible machine commands, which are associated with the loaded conditional command, to the computer. The memory, to which the microcontroller has access, may be particularly a register which is present on the microcontroller.
Due to its mode of operation, the microcontroller according to the invention allows a considerably greater flexibility in its use and in programming without extensive changes in the structure of the hardware being necessary. A conditional command can be used for programming in the same way as conventional assembler commands. When executing the program code, it ensures a greater flexibility because the actually performed instruction depends on the data which are present at the instant of forming this instruction in the memory to which the command decoder has access.
The memory, to which the command decoder has access, is preferably adapted in such a way that it can comprise input data of the microcontroller. Input data of the microcontroller may be particularly digital or digitized information supplied by a connected apparatus.
In accordance with a special embodiment of the invention, the command decoder is adapted in such a way that, dependent on the contents of the memory to which the command decoder has access, the conditional command is decoded as an access command for the computer to different memory types. The access to different memory types, starting from the same conditional command, is a frequently occurring situation of use in which the embodiment of the microcontroller according to the invention is particularly advantageous. Numerous microcontrollers have different assembler commands for access to different memories. For example, the microcontroller 80C51 has the command xe2x80x9cmovxe2x80x9d for moving data memory data and the command xe2x80x9cmovcxe2x80x9d for code memory data. A generic pointer (for example in the high-level language C) which has address-controlled access to the overall implemented memory is possible for such microcontrollers with either considerable assembler code effort or with additional hardware-supported memory configurations (memory mapping). In contrast, the implementation of a data-controlled, conditional command with a single program command allows access to all implemented data memories, because the relevant desired instruction is decoded in dependence upon the data, for example, dependent on the contents of a processor register as a pointer. This operation has the external effect of access to a linear memory. It is therefore a great advantage that, for example, memory management units which are provided can be used without any change in spite of virtual reconfiguration of the memory.